The inhibitory effect of hormones associated with stress on Na appetite ofsheep

Stress is a large stimulus of Na appetite in rabbits, rats, and mice. This study investigated the influence of some peptides implicated in stress, i.e ., adrenocorticotropin (ACTH), corticotropin-releasing factor (CRF), and th e recently discovered member of the CRF family, urocortin, on the ingestive behavior of sheep. Intracerebroventricular infusion of these peptides over 4 days decreased the need-free Na intake of Na-repleted sheep. Intracerebr oventricular infusion of urocortin, however, did not alter Na intake of Na- depleted sheep. Systemic infusion of ACTH increased, whereas systemic infus ion of either urocortin or CRF decreased, Na intake of Na-repleted sheep. T he increase in Na intake caused by the peripheral infusion of ACTH was bloc ked by concurrent i.v. infusion of urocortin, substantiating the inhibitory role of this peptide on Na appetite. Central administration of all peptide s and i.v. administration of urocortin or urocortin and ACTH combined decre ased food intake. Water intake was not directly influenced by the peptides. Rather, decreased water intake, when observed, was secondary to decreased food intake, as determined by pair-feeding experiments. Whereas systemic in fusion of ACTH mimics the increase in Na intake observed in several differe nt stressful situations, CRF and urocortin actually inhibit Na intake, indi cating a direct central action overriding any effect of these peptides on A CTH release. Indeed, the inhibition of Na intake by urocortin occurred desp ite its stimulation of ACTH release and the subsequent increase in peripher al level of cortisol. Thus it would appear that hormones associated with st ress have both excitatory and inhibitory influences on Na intake. Presumabl y, other physiological processes entrained by stress also will be important in determining the quantitative outcome on Na appetite.